ci: install OpenGL/GLFW deps for the Linux viewer instead of SDL2

The interactive frontend moved from SDL2 to GLFW + OpenGL. GLFW is built
from source via CPM, so the runner needs system OpenGL (find_package(OpenGL)
gates IG_HAS_UI) plus GLFW's X11/Wayland backend headers; SDL2 is no longer
used.

Author: PearCoding

.github/workflows/build-linux.yml

@@ -24,7 +24,9 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y --no-install-recommends \
-            ninja-build libtbb-dev zlib1g-dev libsdl2-dev libpython3-dev
+            ninja-build libtbb-dev zlib1g-dev libpython3-dev \
+            libgl1-mesa-dev xorg-dev \
+            libwayland-dev libxkbcommon-dev wayland-protocols extra-cmake-modules
 
       # A complete, self-consistent LLVM + Clang dev toolchain (static libs and
       # cmake config), which the distribution packages do not provide.